The earliest dispersal of humans into North America is a contentious subject, and proposed early sites are required to meet the following criteria for acceptance: (1) archaeological evidence is found in a clearly defined and undisturbed geologic context; (2) age is determined by reliable radiometric dating; (3) multiple lines of evidence from interdisciplinary studies provide consistent results; and (4) unquestionable artefacts are found in primary context1,2. Here we describe the Cerutti Mastodon (CM) site, an archaeological site from the early late Pleistocene epoch, where in situ hammerstones and stone anvils occur in spatio-temporal association with fragmentary remains of a single mastodon (Mammut americanum). The CM site contains spiral-fractured bone and molar fragments, indicating that breakage occured while fresh. Several of these fragments also preserve evidence of percussion. The occurrence and distribution of bone, molar and stone refits suggest that breakage occurred at the site of burial. Five large cobbles (hammerstones and anvils) in the CM bone bed display use-wear and impact marks, and are hydraulically anomalous relative to the low-energy context of the enclosing sandy silt stratum. 230Th/U radiometric analysis of multiple bone specimens using diffusion–adsorption–decay dating models indicates a burial date of 130.7 ± 9.4 thousand years ago. These findings confirm the presence of an unidentified species of Homo at the CM site during the last interglacial period (MIS 5e; early late Pleistocene), indicating that humans with manual dexterity and the experiential knowledge to use hammerstones and anvils processed mastodon limb bones for marrow extraction and/or raw material for tool production. Systematic proboscidean bone reduction, evident at the CM site, fits within a broader pattern of Palaeolithic bone percussion technology in Africa3,4,5,6, Eurasia7,8,9 and North America10,11,12. The CM site is, to our knowledge, the oldest in situ, well-documented archaeological site in North America and, as such, substantially revises the timing of arrival of Homo into the Americas.
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The following individuals worked at the CM site: L. Agenbroad (deceased), B. Agenbroad, J. Mead, M. Cerutti, M. Colbert, C. P. Majors, B. Riney, D. Swanson (deceased) and S. Walsh (deceased). M. Hager was instrumental in ensuring completion of this project. J. Berrian and D. Van der Weele photographed bone and rock specimens and K. Johnson (SDNHM), S. Donohue (SDNHM), C. Abraczinskas (UMMP) and E. Parrish produced various main and Extended Data Figures. E. Hayes, J. Field and V. Rots assisted with photography and interpretation of use-wear on cobbles. C. Musiba and K. Alexander provided photographs of the experimental elephant bone breakage. E. Duke provided the photographs of the experimental anvil wear on bone. Financial support was provided by Caltrans-District 11, P. Boyce and D. Fritsch, The James Hervey Johnson Charitable Educational Trust, The National Geographic Society (Research Grant 4971-93), The Walton Family Foundation (at the recommendation of J. and C. Walton) and the many donors to the Center for American Paleolithic Research. Any use of trade, firm or product names is for descriptive purposes only and does not imply endorsement by the US Government.
Extended data figures
Animation of a 3D surface model of CM-222 (also illustrated in Fig. 2c), an “impact flake” made on cortical bone of Mammut
View using Windows Media Player (select “Repeat” to loop video, showing scale bar at end of each cycle; remove cursor from frame to close progress bar and maximize viewing area) or by dragging file onto an open tab in Chrome (after video starts, right-click within frame, uncheck “Show controls” option and check “Loop” option to watch several cycles). Upper panel of animation shows model with vertex-color; lower panel shows a mostly grayscale model that displays topography more clearly. Color overlay on grayscale model: yellow, impact surface; red, convex ovoidal surface (bulb of percussion; dark color proximal to point of impact; light color distal to point of impact); blue, concave ovoidal surface (negative bulb of percussion; dark color proximal to point of impact; light color distal to point of impact); dotted blue line, margin of hinge fracture at periphery of negative bulb. Symmetry axis of ovoidal impactor indicates trajectory of impact responsible for flake. See caption of Fig. 2 for additional annotation. Animation starts with ventral view of flake, rotates to dorsal view showing a negative flake scar and hinge fracture, continues to a slightly elevated lateral view showing topography of both sides of flake and angle of impactor, tilts to look down on hinge fracture, rotates to look down axis of impactor, and then ends looking straight down on the impact surface. This type of flake is clearly produced by percussion.
Animation of a 3D surface model of CM-230 (also illustrated in Fig. 2b), a cone-flake made on cortical bone of Mammut
See description of Supplementary Video 1 for viewing directions, general description of animation, and colour code for lower (grayscale) model. Additional annotation in caption of Fig. 2. Pause in animation offers a low-angle view along the ventral fracture surface, showing the convex curvature of a subtle bulb of percussion (red) just below the (yellow) impact surface (no impactor shown with this model, but trajectory of impact would have been normal to impact surface). This type of flake is clearly produced by percussion.
Animation of a 3D surface model of CM-288 (also illustrated in Extended Data Fig. 4a-e), a spiral-fractured piece of cortical bone from one of the Mammut femora
See description of Supplementary Video 1 for viewing directions, general description of animation, and color code for lower (grayscale) model. Animation shows a simple rotation of the models. The grayscale version is portrayed with an abstract impactor and anvil, both of which rotate with the bone fragment. The form of this fragment is characteristic of green-bone fracturing.
Animation of a 3D surface model of CM-340 (also illustrated in Fig. 2d), a large fragment of femoral cortical bone of Mammut
See description of Supplementary Video 1 for viewing directions, general description of animation, and color code for lower (grayscale) model. Animation begins with a simple rotation of the fragment, then zooms in to the area of impact, where two concentric negative (concave) flake scars (light blue patches) bracket a partial, undetached flake, before elevating to show the impact notch on the outer cortical surface (yellow) just above the undetached flake. No impactor is shown with this model, to avoid obscuring detail, but trajectory of impact would have been normal to impact surface. The form of this fragment and impact notch are characteristic of percussion-induced green-bone fracturing.
Animation of a 3D surface model of CM-438a (also illustrated in Fig. 2a), a cone-flake made on cortical bone of Mammut
See description of Supplementary Video 1 for viewing directions, general description of animation, and color code for lower (grayscale) model. Animation starts with a view of the ventral surface, rotates 360º, passing the dorsal surface, then continuing in an upward arc to look down on the cortical (impact) surface, then reversing to return to the starting point. No impactor is shown with this model, but trajectory of impact would have been normal to impact surface. This type of flake is clearly produced by percussion.
Animation of 3D surface models of CM-255, 263a, 263b, 329 and 390, fragments of thick cortical bone (probably femoral) of Mammut
See description of Supplementary Video 1 for viewing directions, general description of animation, and colour code for lower (grayscale) model. Animation shows a 360º rotation of the entire assembly of bone fragments, then shifts to a more elevated perspective for a second 360º rotation. During this second turn, the fragments fly apart and then together again to show how they fit precisely to reconstruct the larger assembly.
Animation of 3D surface models of CM-109, 254, 262, 283, 284, 304 and 423, fragments of a pegmatite hammerstone shown in the map in Fig. 3 (CM-423 is also shown in Extended Data Figs. 3f and 5g,h).
See description of Supplementary Video 1 for viewing directions, general description of animation, and colour code for lower (grayscale) model. Animation begins by rotating about 180º near the equatorial plane of the oblate spheroid this assembly resembles, then rises to look down on this plane. During the next 180º rotation, the fragments fly apart and then together again to show how they fit precisely to reconstruct the original, unbroken cobble.
Video record of experimental breakage of elephant limb bone in Tanzania and later experiments in Colorado, USA.
Multiple impacts with a hafted hammerstone succeed in breaking a femur across a proximal portion of the diaphysis. Later, an unhafted hammerstone is used to remove flakes from the cortical wall of a transversely fractured bone. Replicated green-bone fractures show properties comparable to those of specimens from the Cerutti Mastodon site.
About this article
Successful classification of experimental bone surface modifications (BSM) through machine learning algorithms: a solution to the controversial use of BSM in paleoanthropology?
Archaeological and Anthropological Sciences (2018)